Polymers have been modified with various additives in attempts to reduce the flammability (or increase the combustion resistance). Such additives have included phosphites, phosphates, thiophosphoric acid esters containing halogenated alkyl radicals and other halogenated organic compounds. With many such additives, they must be added at relatively high weight percentages that may adversely affect the physical and/or optical properties of the resulting articles. Polytetrafluoroethylene has been added, as an anti-drip and flame retardant agent, to many polymers, but adversely affects the clarity and transparency of molded articles made therefrom. Glass fibers may be added, but the addition adversely affects the polymer matrix and optical properties. In many applications, polymer compositions are rendered opaque by the addition of pigments to mask the reduced optical properties.
More recently there is an increasing need for new flame-retardants for polymer applications. Although existing products are effective at providing flame retardancy at low cost, concerns have been raised regarding the health and environmental risks as they are considered to be environmentally persistent, bioaccumulative materials. In some European countries there are proposals to ban the use of halogenated and heavy metal containing retardants.